Support gapless playback for mp3 and m4a

Gapless playback for appropriately tagged mp3 and m4a files.
Currently this is implemented in OMXCodec, which most players
use, but should be easy to support in other players as well by
using the SkipCutBuffer utility class.

Change-Id: I748c669adc1cfbe5ee9a7dea2fad945d48882551